In conventional practice, there have been proposed systems that heat water using both refrigerant discharged from a low-stage compressor and refrigerant discharged from a high-stage compressor in a multi-stage compression refrigeration cycle, such as the heat pump water heater disclosed in Japanese Laid-open Patent Application No. 2002-106988, for example.
With this system, not only can the compression efficiency be improved by using a multi-stage compression system in a heat pump circuit, but there is also an attempt to satisfactorily increase energy efficiency by using the refrigerant discharged from the high-stage compressor as well as the refrigerant discharged from the low-stage compressor to heat up hot water for a hot-water supply.
Specifically, this system uses a configuration wherein a valve is provided so as to branch the flow of water for the hot-water supply, one flow of hot water is heated by the refrigerant discharged from the high-stage compressor, and the other flow of hot water is heated by the refrigerant discharged from the low-stage compressor. From the perspective of satisfactorily increasing the cycle efficiency, it is proposed that the branched flow ratio of water for the hot-water supply would preferably be such that the other flow heated by the refrigerant discharged from the low-stage compressor is set to half or less of the total water amount.